Vehicle bumper system

ABSTRACT

A vehicle bumper system defined principally by outboard and inboard elongate beams which project transversely across the vehicle. The ends of the front and rear beams are joined by connecting points which function as energy-absorbing fulcrums or hinges, with the remainder of the front and rear beams initially being free of direct structural connection. The front beam is outwardly curved so that the center portions of the front and rear beams define a gap therebetween. The rear beam has connections to the vehicle at two points spaced transversely inwardly from the end connections, which connections define inboard fulcrum or hinge points. The front and rear beams are each formed as elongate monolithic structures, such as of high strength steel, and have configurations which enable them to nest one within the other in the longitudinal direction of the vehicle.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC §119(e) of copendingprovisional application Serial No. 60/350,725 filed Jan. 22, 2002, theentire disclosure of which is herein incorporated by reference.

FIELD OF THE INVENTION

This invention relates to a bumper system for a vehicle and, morespecifically, to an improved bumper system which can be constructed ofsmall package size while providing high energy absorption capability.

BACKGROUND OF THE INVENTION

Bumpers are used on motor vehicles to absorb low level impact forces andto limit the amount of damage sustained to the vehicle body during highlevel impacts. In an attempt to achieve this objective, many of theknown bumper systems have necessarily resulted in arrangements involvingan undesirably large size or space requirement, and in addition haveresulted in undesired structural complexity and cost. In addition, it isbelieved that most such bumper systems have failed to provide formaximum energy absorption resulting from an impact, particularly inrelationship to the overall size, weight, cost and protectability of theknown bumper systems.

Conventional design practice is to provide a bumper system having asingle armature (i.e., a simple beam) which, when impacted, absorbsenergy by permitting buckling (i.e., plastic deformation) at locationsconcentrated at the vehicle centerline of the beam and at the locationswhere the beam mounts to the vehicle. This arrangement of the simplebeam, however, provides an inefficient energy absorbing capability, andhence the bumper system is conventionally provided with separate energyabsorbers such as struts, springs or foam members which cooperate withthe beam. This conventional design is thus complex and requiressignificant space to package it on a vehicle, and generally results inan inefficient use of material and often results in a system havingsignificant weight.

The present invention relates to an improved bumper system for a vehiclewhich attempts to improve on conventional prior art constructions byproviding a multiple-beam bumper system which, in conjunction with theconnections to the vehicle, define multiple fulcrum points so that thebumper system is effectively defined by multiple beams which permit moreeffective absorption of energy, as caused by an impact against thebumper, due to relative movements of the beams and the permissibleplastic energy-absorbing deformations which occur within the bumpersystem.

The bumper system of the present invention, as aforesaid, in addition topermitting more effective dissipation of energy within the bumper systemprior to the ending of an external impact event, is also believed torepresent a bumper system solution which can be more readily and lessexpensively manufactured and can be incorporated into a smaller packagedepth by permitting more energy to be dissipated per unit distance ofimpact intrusion.

In the improved vehicle bumper system of this invention, the system isdefined principally by outboard (i.e. front) and inboard (i.e. rear)elongate beams which project transversely across the vehicle. The endsof the front and rear beams are joined by connecting points whichfunction as energy-absorbing fulcrums or hinges, with the remainder ofthe front and rear beams initially being free of direct structuralconnection. The front beam is preferably of an outwardly curvedconfiguration so that the center portions of the front and rear beamsdefine a horizontal space or gap therebetween. The rear beam defines thestructural connection to the vehicle, and in particular the rear beam attwo points disposed on opposite sides of the vehicle longitudinalcenterline, and spaced transversely inwardly from the end connections,is joined to mounting elements or rails on the vehicle by connectionswhich define inboard fulcrum or hinge points. The front and rear beamsare each preferably formed as elongate monolithic structures, such as ofhigh strength steel, and have configurations which enable them to nestone within the other in the longitudinal direction of the vehicle. Forexample, one of the beams is preferably of a C-shaped cross section, andthe other beam is of a compatible C-shaped or hollow rectangularconfiguration to enable the two beams to at least partially nest. Thetwo beams, in the nondeformed condition, have the end parts thereofnested together to define the outboard connections thereat. An externalimpact against the front beam can effect rearward deflection thereof andtransmission of energy along the front beam to the outboard connections,which in turn effect energy absorption at the end beam portions of therear beam which project between the inboard and outboard connections.This also causes the center portion of the rear beam to deflectforwardly toward the front beam to effect additional energy absorption,with the front and rear beams being moved toward one another for moreeffective nesting engagement so that the two beams ultimately act as oneso as to permit additional absorption of the impact energy. Additionalconnecting blocks can be provided for cooperation between the front andrear beams if desired.

In the improved bumper system of the present invention, as aforesaid,the front and rear beams and their connections to one another at theoutboard ends, and the connection of solely the rear beam to the vehicleat the inboard connection points, effectively define a kinematicstructure having four connection points which function similar tofulcrums in that they permit energy-absorbing relative motion betweenthe front and rear beams, and between the rear beam and the vehicleframe, with the energy absorption being in various stages as the impactevent progresses. Further, the four connection points effectively causethe front and rear beams to define a four-beam system, with the rearbeam having three beam portions due to the pairs of inboard and outboardconnection points. This in addition enables the center beam portion ofthe rear beam to undergo outward bowing or deflection (i.e. away fromthe vehicle) toward the front beam during an impact event so as toimprove the energy-absorbing capabilities while at the same timeminimizing or delaying the impact of the bumper against the remainder ofthe vehicle.

Other objects and purposes of the improved bumper system according tothe present invention will be apparent to persons familiar with systemsof this general type upon reading the following specification andinspecting the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an improved bumper assembly according tothe present invention.

FIG. 2 is a diagrammatic plan view illustrating the inventive bumpersystem and its connection to a vehicle.

FIG. 3 is an enlarged cross-sectional view taken along line 3—3 in FIG.2 and showing the cross section of the front and rear beams.

FIG. 4 is a view similar to FIG. 3 but illustrating a variation in thebeam cross sections.

FIG. 5 is a further view similar to FIG. 3 and illustrating a furthervariation of the beam cross sections.

FIG. 6 is a perspective view similar to FIG. 1 but illustrating a bumpersystem having contact blocks associated with the rear beam.

FIG. 7 is an enlarged central cross-sectional view of the bumper systemof FIG. 6.

Certain terminology will be used in the following descriptions forconvenience in reference only, and will not be limiting. For example,the words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” willrefer to directions in the drawings to which reference is made. The word“front” will refer to a direction which faces away from the vehicle end,namely upwardly in FIG. 2, and the word “rear” will refer to theopposite direction. The words “inwardly” and “outwardly” will refer todirections toward and away from, respectively, the geometric center ofthe bumper system and designated parts thereof. Said terminology willinclude the words specifically mentioned, derivatives thereof, and wordsof similar import.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2, there is illustrated an improved vehiclebumper system 11 according to the present invention. The bumper assembly11 is adapted to be mounted on the front and/or rearward end of avehicle, the frame or basic structure of which is diagrammaticallyindicated at 12 in FIG. 2.

The bumper assembly 11 is made up principally of two main elongate beamsor armatures, namely a rigid front or outboard beam 13 and a rigid rearor inboard beam 14, the latter being interposed in the space between thefront beam 13 and the vehicle. The beams 13 and 14 project generallyhorizontally and transversely with respect to the longitudinal directionof the vehicle, namely the typical direction of vehicle movement, and inplan view as illustrated in FIG. 2 are symmetrical with respective tothe longitudinal centerline 15 of the vehicle.

The front beam 13, adjacent opposite free ends thereof, has end portions16 which are joined by end connections 17 to respective end portions 18defined at opposite free ends of the rear beam 14. The end connection 17defines a relatively rigid connection between the ends of beams 13 and14 so that these beams can relatively rotate or angularly displace atthis end connection only in response to application of a significantforce-created moment which provides energy absorption and transmissionas the bumper assembly deflects and deforms in response to an externalimpact against the front beam 13. The end connectors 17 thus function asenergy-absorbing vertical fulcrums which will typically permit relativeangular displacement between the beams in response to application ofsufficient energy as to cause plastic energy-absorbing deformation. Theend connections 17 provided between the ends of the front and rear beamsis the principal structural connection between these elements.

The rear beam 14 in turn provides the principal structural connection tothe vehicle, such as to a pair of frame or mounting members (i.e. rails)23 which are associated with the end of the vehicle for connection tothe bumper system. The vehicle mounting members 23 are disposed spacedfrom and typically symmetrically on opposite sides of the centerline 15,and connect directly to the rear beam 14 by connections 24 whichpreferably function as vertical fulcrums or hinges.

The pair of connections 24, herein referred to as inboard connections,are spaced inwardly relative to the end or outboard connections 17,whereby the connections 24 have no direct contact or engagement with thefront beam 13 when the bumper assembly is in a non-deformed condition.This disposition of the inboard and outboard connections 24 and 17,respectively, causes the rear beam 14 to be effectively divided intothree beam portions, namely an elongate center portion 21 which extendsbetween the connection points 24, and a pair of end beam portions 19which extends between the inboard connections 24 and the adjacentoutboard connections 17.

The front beam 13, in a generally horizontal plane, is preferablyprovided with an outwardly curved or arcuate shaped configurationthroughout the lengthwise extent thereof so that it bows or curvesoutwardly in the longitudinal direction of the vehicle. The rear beam 13may be straight as illustrated, or may be provided with a forwardarcuate or outwardly bowed configuration if desired, although thearcuate shape of the inboard or rear beam 14 would be less than that ofthe front or outer beam 13. The configuration of the beams 13 and 14when in the assembled state, and prior to being subjected to an externalimpact, is such that the center portion of the front beam 13 is spacedforwardly from the center portion 21 of the rear beam 14 so as to definea horizontal gap or space 22 therebetween.

The front and rear beams 13 and 14 are preferably provided withthree-dimensional cross sections which, at least in part, involve aC-shaped configuration so as to permit the front and rear beams toeffectively nest one within the other, which nesting relationship existsinitially only at the ends 16 and 18.

More specifically, as illustrated by FIG. 3, the front beam 13 in onepreferred embodiment of the invention has a generally C-shaped crosssection which opens rearwardly and is defined by a upright front wall 26which, at upper and lower ends, joins to rearwardly projecting top andbottom walls or legs 27. The rear beam 14 is of a similarrearwardly-opening C-shaped cross section defined by an upright frontwall 28 which at upper and lower edges is joined to rearwardlyprojecting top and bottom walls or legs 29. The overall height of therear beam 14 is selected so as to permit it to move into the interior of(i.e., nest within) the front beam 13, the latter having sufficientspacing between the inside surfaces of the top and bottom walls 27 so asto permit the rear beam 14 to be positioned therebetween. This nestingrelationship enables the ends 16 and 18 to nest together and permit thefront and rear beams to be joined at the connections 17, whichconnections will typically exist between the overlapping top and bottomwalls 27 and 29. The center portions of the beams, however, will bespaced apart as illustrated in FIG. 2, and as illustrated in FIG. 3wherein the front beam 13 is spaced forwardly from the rear beam 14.

If desired, the overall structural properties of the rear beam 14 can befurther enhanced by forming same as a closed tube of generallyrectangular cross section. This is achieved in the illustratedembodiment by closing off the C-shaped rear beam by means of a back wall25, the latter having flanges which can be suitably fixed, as bywelding, to the top and bottom walls 29. Alternately, the rectangularprofile of the rear member 14 in FIG. 3 can be formed using otherstructural techniques, such as by roll forming the rectangular tube andthen longitudinally seam welding same.

As a modification which effectively is a reversal of the arrangementshown in FIG. 3, the front and rear beams can be constructed asillustrated in FIG. 4. In this variation, the front beam 13′ has agenerally rectangular tubular cross section defined by front and rearwalls 31 and 32 respectively, joined by top and bottom walls 33, and therear beam 14′ is a forwardly opening C-shaped cross section defined byan upright rear wall 34 joined to forwardly projecting top and bottomwalls 35. The interior of the C-shaped rear beam 14 is sized so as topermit the tubular front beam 13′ to nest within the rear beam 14′.

A still further variation of the cross section of the front and rearbeams is illustrated in FIG. 5. In this variation the front beam 13″ andrear beam 14″ are both of a hollow tubular cross section configured tonest one within the other. More specifically, the front beam 13″ is ahollow C-shaped member which opens rearwardly and is defined by spacedouter and inner upright front walls 41 and 42 respectively, and thefront beam has rearwardly projecting channel-shaped hollow legs definedby outer top and bottom walls 43 which join to the outer front wall 41,and inner top and bottom walls 44 which join to the inner front wall 42,with the hollow legs being closed off at rearward ends by rear walls 45.The rear beam 14″ is of a rectangular tubular cross section defined byupright front and rear walls 47 and 48, respectively, rigidly joined bytop and bottom walls 49. The height of the rear beam 14″ is such as topermit it to nest within the interior of the C-shaped front beam 13″,generally in the recess defined between the upper and lower walls 44.

The front and rear beams 13 and 14, including the variations suggestedby FIGS. 3-5, are preferably individually constructed as one-piecemonolithic elongate metal members, preferably high strength steel of atleast 100 ksi yield strength, with the beams preferably being rollformed so as to provide the beams with desirable shape and strengthproperties. The front and rear beams 13 and 14 are assembled together,such as through the outboard connectors 17, such that each of the beams13 and 14 in the assembled condition is in its preformed and hencenon-stressed shape. As to the fulcrum connectors 17, they will typicallybe a rigid or semi-rigid connector which will provide or permit aspringlike connection between the front and rear beams adjacent the freeends thereof so that, upon application of an impact force against thefront beam, the front beam can deflect inwardly and simultaneouslyeffect transmission of impact energy lengthwise along the beam into theoutboard connectors 17 associated with opposite sides of the bumperarrangement. These connectors 17, such as elastically and/or plasticallydeformable springlike hinges, permit appropriate deflection and movementat the connector so as to absorb additional energy, and at the same timethe end beam portions 19 associated with the rear beam 14 canelastically and plastically deflect or deform rearwardly about theinboard connection points 24. This latter deflection will typically beaccompanied by forward deflection or bowing of the rear center beamportion 21 toward the center portion of the front beam 13, with thisforward deflection of the center rear beam portion 21 effectingabsorption of additional impact energy.

As the impact energy continues to be applied to and absorbed in thebumper system, the opposed center portions of the front and rear beamsboth move, and effectively move in opposite directions toward oneanother until the center portions effectively nest one within the other.At this stage the front and rear beams thus effectively function as asingle beam and are effective for absorbing additional impact energy asthe nested center portions of the front and rear beams are deflectedrearwardly.

The overall bumper assembly and specifically the construction employingfront and rear beams coupled principally by the two outboard connectionpoints 17, and the coupling of the rear bumper member 14 to the vehiclethrough the two inboard connection points 24, thus effectively providesa four-point kinematic action which enables the impact energy to beprogressively absorbed as a result of movement and deformation of thedifferent parts of the front and rear beams in response to an externalimpact against the front beam. At the same time, the fact that the rearbeam is initially deflected outwardly away from the vehicle intoengagement with the front beam, prior to its thereafter beingeffectively coupled with the front beam and deflected inwardly towardthe vehicle for further energy absorption, is believed to permit ahigher quantity of energy to be effectively absorbed within the bumpersystem prior to impact of the bumper against the vehicle, with theoverall bumper system still occupying only a minimum space envelope whenmounted on the vehicle.

Considering in greater detail the energy-absorbing end connections 17which join the ends of the outboard beam 13 to the respective ends ofthe inboard beam 14, this connection 17 preferably provides significantrotational resistance between the connected ends of the beams 13 and 14such that a significant force-created moment is required to effectangular displacement of the connected ends of the beams 13 and 14, whichin turn results in significant absorption of impact energy as imposed onthe bumper system. This energy-absorbing end connection 17 hence mayabsorb some energy due to elastic deformation of the material associatedwith the beams or the end connection, but more significantly causesenergy absorption due to plastic deformation of the material.

The end connection 17, in a typical and practical construction of thebumper assembly, may be created by a welded connection between the beams13 and 14 adjacent the free ends thereof. Such welded connection ispreferably defined by a horizontally elongated weld, and more preferablya vertically-spaced pair of horizontally-elongated welds which connectthe ends of the two beams 13 and 14 together. For example, with thearrangement illustrated by FIGS. 1-3, a first horizontally-elongate weldcan be provided at the cooperating ends of the beams between the topwall of the rear beam and the top leg of the front beam where thesebeams nest together, such weld being diagramatically indicated at 20 inFIG. 2, and a similar horizontally-elongate weld can be provided betweenthe bottom wall of the rear beam and the lower leg of the front beam.Such weld arrangement, and the end connection defined thereby, henceprevents relative horizontal translation between the ends of the beamsdue to imposition of an external impact against the bumper system, andat the same time may permit limited angular displacement between theends of the connected beams due principally to plastic deformation ofthe beam material in the vicinity of the end connections, which plasticdeformation is effective for absorbing at least some of the externalimpact energy while permitting other external impact energy to betransmitted through the connection to the inboard beam.

In place of an end connection employing welds as described above, theend connection 17 may involve some type of mechanical interlock betweenthe cooperating ends of the beams, such as a tab on one beam projectinginto a slot or groove on the other beam, so as to function in generallythe same manner as described above. Further, the mechanical interlockmay involve some type of connecting pin or coupling member, such as asquare or non-round pin or a press or interference fit pin, whichimposes substantial resistance against relative rotation between theconnected ends of the beams 13 and 14, which connector hence resistsrelative translation and/or rotation between the connected ends butpermits energy absorption at the connection due to plastic deformationof material associated with the end parts of the beams and/or theconnector.

As a still further alternative, the end connector 17 joining the endparts of the beams 13 and 14 may comprise a heavy-duty spring shaped andconfigured to provide generally the same energy-absorbing function asdescribed above. For example, the spring ends can be anchored or fixedto the connected end parts of the beams.

Regarding the connections 24 between the inboard beam 14 and the framerails 22, these connections will preferably be initially designed so asto optimize the ability of the inner beam to transmit energy from theend parts to the center part thereof while at the same time permittingthe inner beam to effectively absorb impact energy at both the end oroutboard parts as well as in the center part thereof. The connection 24will preferably provide resistance against at least horizontaltranslation or horizontal rotation so as to permit at least some of theenergy transmitted to the outboard parts of the inboard beam 14 to betransmitted along the beam into the center part thereof. The connection24 may comprise vertical hinge pins which will hence permit limitedhorizontal rotation but prevent horizontal translation.

As a further and preferred construction in terms of simplicity ofvehicle manufacture and assembly, the connection 24 may involve a weldedconnection between the inboard beam 21 and the rail 22, which weldedconnection may be similar to spot welds at the points 24, or whichwelded connection may be defined by a vertically elongate weld betweenbeam 21 and rail 22 which will be effective in preventing relativetranslation movement but at the same time may permit plastic deformationin the beam at the weld similar to a horizontal flexing movement due tothe plastic deformation of the material in the vicinity of the weld.Such vertically elongate weld is diagrammatically shown at 30 in FIG. 2.

Referring to FIG. 2, there is illustrated a variation of the bumperassembly 11 which permits some of the impact forces applied to the outerbeam 13 to be short circuited and communicated directly to the rear beam14 without passing through the end connectors 17. In this variation, aforce communicator structure 53, as indicated by dotted lines in FIG. 2,can be disposed within the gap 22 for connection between the front andrear beams at locations spaced inboard from the end connectors 17. Thecommunicator member 53 will typically be sandwiched between the frontand rear beams 13 and 14 to provide a partial force-transmitting shortcircuit from the front beam 13 through the member 53 to the rear beam14, whereby some impact force and energy hence will be transmittedthrough the communication member 53, and other of the impact energy willtransmit along the beam 13 to the end connectors 17 for application tothe ends of the rear beam 14 in the same manner as described above.

The communicator member 53 may be formed as one or more deformable foamor plastic or metal members for connection directly between the frontand rear beams and, for example, for connection directly between thecenter beam portions of the front and rear beams. The communicator 53will typically be engaged with the rear beam 14 at one or more locationspositioned inwardly from the inboard connectors 24. The foam connectormember 53 may be of a crescent shape so as to occupy substantially theentire gap between the beams 13 and 14. It will be appreciated that thecommunication member 53 will permit only part of the impact energy to betransmitted therethrough, and that the geometry of the bumper assemblywill be effective with respect to the remaining impact energy so thatthe bumper assembly functions in the same manner as if the communicator53 was not present, such as described above.

Referring now to FIGS. 6 and 7, there is illustrated a modified bumperassembly wherein, in this arrangement, the bumper assembly is defined bya front beam 13″ and a rear beam 14″ which are operatively coupled andmounted in the same manner as illustrated by FIG. 2, and generally havecross sections similar to that illustrated by FIG. 5. In this variation,however, the rear beam 14″ has communication or contact blocks ormembers 51 fixedly mounted thereon in the vicinity of the center of thebeam (i.e., substantially at or adjacent the longitudinal centerline15), and these communication blocks 51 are fixedly secured to andrespectively project upwardly and downwardly from the upper and lowerwalls of the rear beam at a location close to the front wall. With thisarrangement, the communication blocks 51 are oriented such that, uponrelative deflection of the center portions of the front and rear beamsso that they relatively move toward one another into a nesting position,the communicator blocks 51 on the rear beam will contact the rear wallassociated with the legs of the front beam, prior to the rear beam fullynesting within the front beam, thereby effectively providing a solidconnection between the center portions of the front and rear beams. Atthis stage the front and rear beams hence effectively function as asingle beam so as to effect continued absorption of energy associatedwith the impact event. This latter stage, wherein the communicationblocks 51 contact the rear wall of the front beam, require that thebumper assembly undergo the various energy-absorbing deflecting anddeformation stages described above, namely the initial deformation ofthe front beam followed by deformation of the rear beam and outwardbowing of the center portion thereof, so as to cause the communicationblocks 51 to contact the front beam so that the two beams thereaftereffectively act in unison with respect to further energy absorption.

With the improved bumper assembly of the present invention, the outboardconnectors 17 can be effectively tuned during the initial design thereofso as to optimize the moment and hence energy applied from the frontbeam to the rear beam in accordance with the overall geometry of thebumper system, which tuning can be accomplished by the overall initialdesign of the connector 17 with respect to the degree of rigidity andelasticity incorporated therein. In addition, the C-shaped and hollowcross sections contemplated for use in forming the front and rear beamsalso permit the desired absorption of energy due to the deformation ofthe beam cross-sections, and these configurations together with thecoupled relationship of the inner and outer beams and the four-pointkinematic connections defined by the connectors 17 and 24 hence maximizethe energy absorption capability of the bumper system, and hence theenergy absorbing capability thereof prior to the bumper deforming intocontact with the end of the vehicle.

While the bumper system in the illustrated embodiments has the ends ofthe front and rear beams connected at the connectors 17, it will berecognized that one of these beams may have ends which overhang orproject outwardly beyond the connectors 17 without detracting from thefunction of the bumper system as summarized herein.

As is conventional, the front beam 13 can be provided with a suitablecovering or cap, such as of a plastic material or the like, so as toprovide the bumper with the desired styling and color consistent withthe desired visual aspects of the vehicle.

Although a particular preferred embodiment of the invention has beendisclosed in detail for illustrative purposes, it will be recognizedthat variations or modifications of the disclosed apparatus, includingthe rearrangement of parts, lie within the scope of the presentinvention.

What is claimed is:
 1. A vehicle bumper system comprising: an elongatemonolithic one-piece outer bumper beam having an upright front walljoined between rearwardly projecting top and bottom walls; an elongateone-piece inner bumper beam positioned adjacent but rearwardly of saidouter bumper beam, said inner bumper beam having end parts at oppositeends thereof which are joined to respective opposite end parts of saidouter bumper beam by end connections which permit at least limited forcemoment-induced, energy-absorbing flexing between adjacent end portionsof said outer and inner beams, said end connections being positionedsubstantially symmetrically on opposite sides of a centerplane of saidbumper system; said inner beam being connected to a vehicle solely attwo connecting points which are positioned on opposite sides of saidcenter plane and are each spaced inwardly from a respectively adjacentsaid end connection, said outer beam being free of direct connection tosaid vehicle; said outer beam being of a preshaped horizontally bowedconfiguration so that an elongate center beam section thereof is bowedoutwardly and is physically spaced forwardly from a center beam part ofsaid inner beam which extends between said connecting points; one ofsaid beams comprising a hollow tube having a generally rectangular crosssection, the other of said beams including a cross section which isC-shaped and opens horizontally toward said one beam and is sized topermit at least partial front-to-rear nesting with said one beam, andsaid end parts of the outer and inner beams being nested one within theother at said end connections; and said outer beam, when subjected to aninward impact, effecting transfer of impact forces along the outer beamto the end connections to cause the center beam part of the inner beamto bow forwardly toward the center beam section of said outer beam.
 2. Avehicle bumper system according to claim 1, wherein the inner beamincludes a pair of cantilevered end beam parts which each extend fromone connecting point to the adjacent end connection, said end beam partsof said inner beam elastically deflecting rearwardly about therespective connecting point as the center beam part bows forwardly inresponse to imposition of an external impact against said outer beam. 3.A vehicle bumper system according to claim 1, wherein each of said beamscomprises a one-piece roll formed steel member, and each of said beamshas a yield strength of at least 100 ksi.
 4. A vehicle bumper systemaccording to claim 3, wherein a deformable energy-absorbingcommunication member is connected between said center beam section andsaid center beam part to permit limited direct energy transfertherethrough upon external impact against said outer beam, and/or ablocking member is mounted on one of said center beam section and saidcenter beam part and is positioned for blocking engagement with theother of said center beam section and said center beam part as they movetoward one another.
 5. A vehicle bumper system according to claim 2,wherein said outer beam is C-shaped in cross section and defines anelongate recess which opens rearwardly toward said inner beam; whereinsaid inner beam comprises said hollow tube which is sized such that theend beam parts thereof are nested within said recess; and wherein saidouter beam is preshaped into a horizontal arc-shaped configuration sothat the center beam section is bowed horizontally forwardly away fromsaid inner beam and is maintained in a generally non-deflected conditionwhen assembled with said inner beam.
 6. A vehicle bumper systemaccording to claim 5, wherein each of said outer and inner beams is ofsubstantially uniform cross section throughout the lengthwise extentthereof.
 7. A vehicle bumper system according to claim 5, wherein eachsaid end connection comprises a first fulcrum-like connection defined bya weld between said inner and outer beams.
 8. A vehicle bumper systemaccording to claim 5, wherein each said connecting point comprises asecond fulcrum-like connection defined by a weld between said inner beamand mounting part on said vehicle.
 9. A vehicle bumper system accordingto claim 8, wherein each said end connection comprises a firstfulcrum-like connection defined by a weld between said inner and outerbeams.
 10. A vehicle bumper system according to claim 1, wherein eachsaid end connection comprises a first fulcrum-like connection defined bya horizontally elongate weld between said inner and outer beams.
 11. Avehicle bumper system according to claim 10, wherein each saidconnecting point comprises a second fulcrum-like connection defined by avertically elongate weld between said inner beam and a vehicle mountingpart.
 12. A vehicle bumper system according to claim 1, wherein eachsaid connecting point comprises a fulcrum-like connection defined by avertically elongate weld between said inner beam and a vehicle mountingpart.
 13. A vehicle bumper system according to claim 1, wherein saidcenter beam part and said center beam section can relatively move intoat least partial nested engagement with one another in response to anexternal impact on said outer bumper beam.
 14. A vehicle bumper systemaccording to claim 1, wherein said other beam of C-shaped cross sectioncomprises said outer bumper beam, and wherein said one beam comprisingsaid hollow tube defines said inner beam.